Many types of fluidics technologies exist, and they are designed to move fluid from one location to another within a fluidics cartridge. Some fluidics cartridges use droplet actuators to move individual droplets within the fluidics cartridge, for example by electrowetting. An electrowetting fluidics cartridge is one example of a digital fluidics technology and typically includes one or more substrates configured to form a surface or gap which holds the reaction droplets that are moved from one location to another. The substrates establish a droplet operations surface, or gap, and can include electrodes arranged in predefined patterns to conduct the droplet operations via electrowetting. In some electrowetting devices, the gap between the substrates is filled with a filler fluid such as oil that is immiscible with the liquid that forms the droplets.
Conventional fluidics cartridges such as used in electrowetting devices are designed to be used in the horizontal position. However, a limitation exists for horizontal fluidics cartridges in that there is a head height restriction of about 3 mm. Thus, a reservoir for holding liquid reagents cannot generally be allowed to hold more than an approximately 3 mm height of liquid. When the height of the liquid becomes greater than about 3 mm in height, the pressure head of the liquid may exceed the force that an electrowetting pad can withstand, causing the reagent to flood the cartridge with liquid. In sequencing by synthesis (SBS) applications, large volumes of reagent (e.g., 50-80 ml) can be preferred. Spreading the large reagent volume over a reservoir area that is only about 3 mm high can consume a large amount of real estate in the fluidics cartridge.
FIG. 1A illustrates a block diagram of an example of a microfluidics system 100 that uses a prior art fluidics cartridge 105 held horizontally or substantially horizontally. In this example, microfluidics system 100 comprises an instrument 110 that has an instrument deck 115 for holding conventional fluidics cartridge 105. Conventional fluidics cartridge 105 can be, for example, any digital fluidics cartridge or droplet actuator cartridge by which droplets and/or volumes of liquid can be processed using droplet operations (e.g., electrowetting). Microfluidics system 100 further comprises a controller 120 for managing the overall operations of microfluidics system 100. Control information is passed from controller 120 to instrument 110 and instrument deck 115. Instrument 110 and instrument deck 115 provide the electrical, mechanical, and fluidic platform for interfacing with conventional fluidics cartridge 105. Associated with instrument 110 is a horizontal plane HP and a vertical plane VP wherein conventional fluidics cartridge 105 is held substantially in the horizontal plane HP. Referring now to FIG. 1B is a side view of a portion of an example of conventional fluidics cartridge 105 that is held substantially in the horizontal plane HP. Conventional fluidics cartridge 105 includes a bottom substrate 150 and a top substrate 152 that are separated by a droplet operations gap 154. Droplet operations gap 154 contains filler fluid 156. The filler fluid 156 is, for example, low-viscosity oil, such as silicone oil or hexadecane filler fluid. Bottom substrate 150 can be, for example, a printed circuit board (PCB) that may include an arrangement of droplet operations electrodes 158 (e.g., electrowetting electrodes). Top substrate 152 can be, for example, a plastic or glass substrate. Top substrate 152 may include a ground reference plane or electrode (not shown).
FIG. 1B shows a droplet 160 in droplet operations gap 154. Droplet operations are conducted atop droplet operations electrodes 158 on a droplet operations surface. Namely, in conventional fluidics cartridge 105, droplet operations are conducted along the horizontal plane HP. Conventional horizontally-mounted fluidics cartridges, such as conventional fluidics cartridge 105, are subject to the 3-mm head height restriction with respect to reservoirs (not shown). Further, conventional horizontally-mounted fluidics cartridges, such as conventional fluidics cartridge 105, are sensitive to tilt (not more than 1-2 degrees) and therefore not well suited for mobile applications. Additionally, in conventional horizontally-mounted fluidics cartridges the elimination of air bubbles can be difficult.